Micrograms to Milligrams (µg to mg)

1 microgram equals 0.001 milligrams exactly.

1 microgram = 0.001 milligrams

How to convert micrograms to milligrams

To convert micrograms to milligrams, multiply the number of micrograms by 0.001. This factor is exact. To go the other way, multiply milligrams by 1,000.

milligrams = micrograms × 0.001

Example: 10 micrograms = 0.01 milligrams.

About these units

Microgram (µg)

Metric (SI)Current unit

One millionth of a gram. Used for very small doses such as vitamin B12 and folic acid; often written mcg on labels.

Tiny doses forced the microgram into everyday use. It is one millionth of a gram, written with the SI prefix micro and the Greek letter mu, but that letter caused trouble: handwritten or badly printed, mu can look like a lowercase m, which would turn micro into milli and make a dose a thousand times too large. For that reason the US Institute for Safe Medication Practices and the FDA recommend writing mcg in medical communication, while UK prescribing guidance says microgram should be written out in full rather than abbreviated.

You meet the unit mostly on nutrition labels and in medicine, where amounts such as folic acid and vitamin B12 are given in micrograms. It also matters in laboratories. According to NIST, the old kilogram prototype gave relative uncertainties of a few parts in ten thousand at the milligram level, and fields such as pharmaceuticals and materials science increasingly need dependable accuracy down at the microgram, which was one argument for redefining the kilogram with a fundamental constant. In text where mu is unavailable, people type u or the micro sign instead.

1 microgram = 1×10⁻⁹ kilograms (exactly).

Sources: Wikipedia: Microgram; NIST: Kilogram introduction (SI redefinition)

Milligram (mg)

Metric (SI)Current unit

One thousandth of a gram. Used for medicine doses and vitamins.

No single inventor can be credited with the milligram. It arrived with the metric system that France introduced in the 1790s, where the gram was the basic unit of mass and thousandths of it were named with a prefix. When the International System of Units was later built around the kilogram, the rule against stacked prefixes meant that a millionth of a kilogram is written 1 mg, never a microkilogram, so the milligram remained a gram-based unit even though the gram itself is not the SI base.

A milligram is small enough that doses of medicine and vitamins are measured in it routinely. A US penny weighs about 2.5 g, so a milligram is roughly one 2,500th of a coin. The unit is also at the center of a well-known safety problem: milligram and microgram differ by a factor of 1,000, and the abbreviation mcg for micrograms is used on prescriptions precisely so that a handwritten micro sign cannot be misread as milli. Confusing the two has caused serious medication errors.

1 milligram = 0.000001 kilograms (exactly).

Sources: Wikipedia: Milligram; Wikipedia: Microgram; Wikipedia: Gram

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